Although wind power has the potential to provide a large proportion of the world's electricity needs, the variability in the velocity of the wind often makes it an unreliable power source. In particular, this variability makes it difficult to construct wind-driven power-generating devices that are effective and efficient under all wind conditions. By way of non-limiting example, the devices disclosed in U.S. Pat. No. 3,942,909 to Yengst, U.S. Pat. No. 4,632,637 to Traudt, and U.S. Pat. No. 4,818,181 to Kodric concentrate low and moderate winds to produce power and are designed to fold or feather in high winds; while these techniques protect the structural integrity of the device, they also decrease the device's ability to produce power in high winds. Conversely, by way of non-limiting example, the device disclosed in U.S. Pat. No. 5,391,926 to Staley et al. can harness high winds for power production, but is not capable of generating adequate torque for continual, reliable power generation in low or moderate winds.
One offered solution for the problem of variable wind velocity has been the vertical axis wind turbine (VAWT). Unlike horizontal axis (propeller-type) windmills, VAWTs pivot about a long vertical axis, such that they may face directly into a wind. A VAWT, therefore, can harness wind energy from large columns of air, making them practical for power generation in low and moderate winds. When combined with features that allow a wind-driven power generator to operate robustly in high winds, a VAWT can be used to generate power in a wide range of wind conditions. By way of non-limiting example, one such device is disclosed in U.S. Pat. No. 6,538,340 to Elder. However, given their relative complexity compared to horizontal axis windmills, VAWTs continue to suffer from lower cost efficiency than other alternative energy technologies.
There is a long-felt need for VAWT devices with improved cost efficiency, which preferably would provide continual, reliable power generation in all wind conditions at costs comparable to other alternative energy generation methods, devices, and systems.